An experimental investigation on long-term performance of the wide-shallow bucket foundation model for offshore wind turbine in saturated sand

Abstract The bucket foundation is considered as a promising alternative to conventional foundations for offshore wind turbines (OWTs) due to its cost-effectiveness and high-reliability. The behavior of bucket foundation under static loading has been extensively investigated, while its long-term performance induced by the cyclic loading under the surrounding soil influence lack of study. This study aims to investigate the influence of one-way cyclic horizontal loading on the long-term performance of the wide-shallow bucket foundation (WSBF) model for offshore wind turbine in saturated sand by using single-gravity (1-g) model tests. Specifically, a series of cyclic experiments with varied loading conditions including load magnitude (P), load frequency (f), excitation height (H) and cycle number (N) were conducted to reveal the influence of loading conditions on dynamic characteristics and accumulated rotation of the WSBF model. Furthermore, the regression analysis method based on artificial neural network (ANN) model is proposed to determine the relationship between loading conditions and the long-term performance of the WSBF model. It is shown that the natural frequency rises and damping ratio decreases with the increase of cyclic loading number during the early cyclic stage. Afterwards, there is a declining or stable trend for the natural frequency and a rising trend for the damping ratio of the WSBF model. As for the accumulated rotation, more than 80% foundation rotation occurs in the first hundred cycles, whereas accumulated rotation for rest cycles tends to be small. Finally, multiple regression analysis and sensitivity analysis based on the ANN model are demonstrated to evaluate and predict the changes in long-term performance of the WSBF model with high accuracy in this study.